1. Field of the Invention
The present invention is in the field of insulating devices and, more particularly, a substantially transparent insulating structure, having an infrared reflecting visible light transmitting coating applied to one surface thereof.
2. Description of the Prior Art
It is presently known to provide a substantially transparent multi-pane insulating structure, which functions so as to inhibit transmission of infrared radiation from a warmer region to a colder region. The structure may typically comprise two or more panes, spaced apart by spacers which extend about the top, bottom, and sides thereof so as to form at least one insulating airspace therebetween. The panes may be bonded together, and a frame may extend about the edges thereof. Such a multi-pane structure may comprise a glass door for a refrigerated cabinet or freezer compartment.
Generally, such multi-pane structures provide substantially more insulation than single-pane structures. However, multi-pane structures are also more expensive than single-pane structures. It is therefore desirable to provide a single-pane structure which provides substantial insulation so as to inhibit transmission of infrared radiation from a warmer region to a colder region.
Further, there is a tendency in such insulating structures for the temperature of the surface exposed in use to the warmer region to attain the temperature at which a visibility-impeding layer may form thereon, by virtue of the temperature differential between the warmer region and the colder region. The visibility-impeding layer may take the form of condensation on a refrigerated cabinet glass door, or frost on a freezer compartment glass door. The formation of such layer tends to occur as a consequence of the temperature differential between the warmer and colder regions, by virtue of the fact that the surface exposed in use to the warmer region is generally at a cooler temperature than the ambient air in the warmer region due to heat loss by radiation and conduction. Since the door occupies a substantial portion of the front of the cabinet, formation of the visibility-impeding layer therein prevents customers from viewing products stored and displayed in such cabinet or compartment, and is aesthetically unattractive and unappealing.
To counter the tendency for condensation and frost to form on the surface of the pane exposed in use to the warmer region, it is known in the art to provide electrical heating means which heat such surface. Various types of electrical heating means have been used, including conductive coatings and resistive wires. Preferably, the conductive coating is visible light transmitting, to enable viewing of products stored and displayed in the cabinet or compartment, and is applied to the surface of the pane facing into the airspace for protection of the coating.
Electrical heating means use substantial quantities of electricity in the operation thereof, which is expensive and inefficient. Nevertheless, use of electricity is necessary in presently known devices to prevent formation of the visibility-impeding layer, so that customers may view products stored and displayed in the cabinet or compartment, and to maintain the attractiveness of the panes. Use of substantial quantities of electricity to heat the pane is particularly necessary where the air in the warmer region has a high moisture content.
It is presently further known to provide infrared filtering visible light transmitting means in such structures, to prevent transmission of infrared radiation therethrough while transmitting visible light.
Transmitting infrared radiation into a colder region increases the heat content thereof, necessitating use of substantial quantities of electricity in operating the refrigeration system to remove such heat from the colder region. These problems arise particularly with respect to refrigerators and freezers.
Various types of infrared filtering visible light transmitting means are presently known. One type of such means is an infrared absorber shown, for example, in Brown U.S. Pat. No. 2,444,976. Brown shows an absorption glass including a composition mixed in the batch during manufacture of the glass, which composition absorbs infrared radiation incident thereon. However, infrared absorbing materials, as in Brown, increase the heat content of the structure. A substantial portion of the absorbed infrared radiation is released back therethrough by conduction and reradiation. This substantially reduces the operating efficiency and utility of such means.
Another type of infrared filtering visible light transmitting means presently known comprises film or laminate applied to a surface of a pane. Such means are shown, for example, in Edwards U.S. Pat. No. 3,499,697. Edwards shows a transparent laminate including a pair of panels, a pair of thin plastic films, and multi-layer and single-layer dielectric films, sandwiched together to provide a laminate which selectively transmits visible light and reflects infrared radiation. Here, as in Brown, the reflected infrared radiation is released back by convection and reradiation.
Still another type of infrared filtering visible light transmitting means presently known comprises a multi-pane insulating structure with an infrared filtering film applied to one surface of one of the panes. For example, U.S. Pat. No. 4,035,608, Stromquist, et al., illustrates use of an infrared reflecting visible light transmitting film applied to the inside surface of the second pane from the warmer region, and a first pane adjacent the warmer region electrically heated to prevent formation of a visibility-impeding layer on the outside surface thereof. The heating means are electrically operated, and are used to prevent formation of condensation or frost. Since the heating means require use of electrical energy for operation therefor, the expense of operation thereof is substantial. This is particularly true with respect to refrigerators and freezers, as there are normally substantial temperature differentials between the ambient warmer region and the colder region, and as the panes occupy a very substantial portion of the selectively openable interface between the warmer region which may include humid ambient air, and the colder region. Further, the electrical heating means radiate heat to the second pane, as well as the first, and such heat radiation interferes with and reduces the efficiency of the coating in reflecting infrared radiation.
It is further presently known to provide a guard for a fluorescent lamp in a refrigerated cabinet. The guard extends substantially the length of the fluorescent lamp and is spaced therefrom so as to form an airspace thereabout. In operation of the cabinet, the airspace constitutes a warmer region, and the surrounding refrigerated air constitutes a colder region. The guard is reusable, and typically need not be disposed of when the fluorescent lamp is replaced.
Infrared radiation may be transmitted from the warmer region in the guard-defined airspace to the colder region in the refrigerated cabinet through the guard, heating the colder region and removing heat from the warmer region. Loss of heat to the colder region reduces the efficiency of operation of the fluorescent lamp and increases the heat load in the colder region within the cabinet, reducing the operating efficiency of the refrigerated system while increasing its expense of operation. On the other hand, increased heat in the warmer region within the guard could provide an environment which would increase the efficiency of operation of the fluorescent lamp.
The problems addressed by the present invention include preventing transmission of infrared radiation from a warmer region to a colder region, preventing formation of a visibility-impeding layer on a surface of a structure exposed in use to a warmer region, preventing reradiation of reflected infrared radiation, and enabling transmission of visible light radiation.
It is normally necessary to use a multi-pane insulating structure to provide insulation sufficient to enable efficient operation of a refrigerated cabinet or freezer compartment. However, if a single-pane insulating structure is used pursuant to presently known devices, such structure is substantially less effective than a multi-pane insulating structure in preventing transmission of infrared radiation from the warmer region outside the cabinet or compartment to the colder region inside the cabinet or compartment. On the other hand, if such a multi-pane insulating structure is used, it is substantially more expensive than a single-pane structure.
It is further normally necessary, pursuant to presently known devices, to use electrical heating means to heat the surface exposed in use to the warmer region to a temperature above the temperature at which a visibility-impeding layer forms. This approach imposes expense and inefficiency upon the insulating structure, particularly where there is a large temperature differential between the warmer region and the colder region, and where the warmer region may include humid ambient air.
Still further, presently known fluorescent lamp guard devices transmit heat generated by the fluorescent lamp to the colder air in a refrigerated cabinet, interfering with the most efficient operation of the fluorescent lamp and of the refrigerated cabinet.
Thus, particular problems arise. If a single-pane structure pursuant to presently known devices is used, such structure is substantially less effective than a multi-pane structure to prevent transmission of infrared radiation from a warmer region to a colder region. However, if a multi-pane structure is used, such structure is substantially more expensive than a single-pane structure. Further, if the surface of the insulating structure exposed in use to the warmer region is not heated electrically pursuant to presently known structures, a visibility-impeding layer forms, which prevents customers from viewing merchandise stored and displayed in the colder region. However, if the surface is heated electrically, a substantial expense is incurred as a result of the use of substantial quantities of electricity necessary for operation thereof. Still further, if a guard is used pursuant to presently known structures so as to protect a fluorescent lamp in a refrigerated cabinet, heat in the airspace surrounding the fluorescent lamp is dissipated by transmission thereof into the colder region, which reduces the operating efficiency of the fluorescent lamp. These are the particular problems for which the present invention provides novel solutions.